Contact circuit for short circuiting device



1959 HANS-JOACHIM KLEINVOGEL ETAL' 2,872,634

CONTACT CIRCUIT FOR SHORT CIRCUITING DEVICE Filed March 13, 1956 2Sheets-Sheet 1 1&5

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| \K] I l \ILHA Feb. 3, 1959 HANS-JOACHIM KLEINVOGEL ETAL 2,872,634

CONTACT CIRCUIT FOR SHORT CI RCUITING DEVICE Filed March 13, 1956 2Sheets-Sheet 2 Amy/V675 United States Fatent {35m CONTACT CIRCUIT FORHORT CIRCUETING DEVICE Hans Joachim Kleinvogel, Berlin Siemensstadt,

Dietrich von Haehier, Berlin-Charlottenhurg, many, assignors toSiemens-Schucirertrverlre in. Berlin and Erlangen, many and (Ger- G.,Germany, a corporation of Ger- My invention relates to a circuit forinitiating the operation of a short circuiting device for shortcircuiting the contacts of contact converters of the type shown incopending application Serial No. 301,880, filed July 31, 1952, nowPatent No. 2,759,128.

Contact converters of the type referred to above utilize a pair ofcooperating contacts for synchronously connecting and disconnecting anA.-C. source and D.-C. load whereby an average voltage is impressedacross the D.-C. load. Contact operation is carried out under as low acurrent as possible so that appreciable contact life may be attained. Tothis end, commutating reactors of the type described in U. S. Patent No.2,693,569, to E. i. Diebold are connected in series with the cooperatingcontacts to ensure a step of current of relatively low magnitude inwhich the contact may be safely operated.

In the event of a fault or so-called are back, in order to preventdamage or destruction of the contacts, a short circuiting meanstherefore is usually provided, the operation of which is initiated by ameans which senses this fault condition.

In the past, circuit means for sensing the fault condition andinitiating the operation of the short circuiter are operative only aftera contact is disengaged under fault conditions or disengaged at a timeafter the protective step of the commutating reactor has ended.

The principle of my invention is to provide circuit means which isoperative to sense fault conditions even before the contact hasdisengaged, as well as after the contact has disengaged if the faultoccurs at this time so that the short circuitiug protective means isenergized as soon as possible.

More specifically, I provide within my novel circuit a first means todetermine the point at which the commurating reactor step occurs and asecond means to determine the point at which the contact is opened. Ithen compare these two times and if they do not coincide, then the shortcircuiter operation is initiated. Hence, if the contact is opened priorto the commutating reactor protective step, the short circuiter will beinitiated at this very early time to thereby provide subsequentprotection for the contact in the faulted phase as well as protectionfor contacts of any other phases present in the converter device.Similarly, if the contact opens after the protective step has ended,then as in the prior art protective means, my novel circuit will causeoperation of the short circuiter for subsequent contact protection.

Accordingly, a primary object of my invention is to provide anenergizing means for short circuiting devices.

Another object of my invention is to provide an energizing means for theshort circuiter of a contact converter wherein a signal will beinitiated if the cooperating contact is opened prior to a low currentstep.

A still further object of my invention is to provide an energizingcircuit for short circuiters which initiates oper ation of the shortcircuiter when the contact is opened 2,872,634 Patented Feb. 3, 1959either before the low current protective step or after the low currentprotective step.

Another object of my invention is to provide a circuit for operating ashort circuiter device which measures the interval during which acommutating reactor is unsaturated and if the contact in series with thecommunicating reactor is not opened within this interval, will thendeliver a signal to operate the short circuiter.

These and other objects of my invention will become apparent when takenin conjunction with the drawings in which:

Figure 1 shows the current time characteristic of the current throughthe contact of a mechanical converter wherein contact interruptionoccurs within the low current step.

Figure 2 is similar to Figure 1 and shows contact interruption occurringafter the end of the low current step.

Figure 3 is similar to Figures 1 and 2 and shows the point of contactinterruption occurring prior to the beginning of the low current step.

Figure 4 shows a first embodiment of my novel circuit when taken inconjunction with a three-phase mechanical rectifier.

Figure 5A shows the voltage time characteristic of the voltage appearingon the auxiliary winding of the commutating reactors of Figure 4.

Figure 5B shows the voltage time characteristic of the voltage inducedin the circuit of Figure 4 for indicating the point of contactinterruption.

Figure 5C shows the voltage time characteristic of the resultant signaldue to the voltage of Figure 5B.

Figures 6A and 6B show how the signal due to' the commutating reactorstep and the signal due to the point of contact interruption arecombined under normal contact interrupting conditions.

Figures 7A and 7B are similar to Figures 6A and 6B but are for thecondition of contact interruption at a point prior to the initiation ofthe low current step.

Figure 8 shows a second embodiment of my novel invention wherein thecircuitry for measuring the contact interruption point has been variedfrom that shown in Figure 4.

Figure 9 shows a still further embodiment of my novel invention whenadapted to a converter having first contacts for making operation andsecond contacts for breaking operation.

Referring first to Figures 1 through 3, there is shown a currentcharacteristic of the current passing through the contact of a converterdevice, this current being identified by the letter I. At the time r itis assumed that a contact of a succeeding phase is closed and thecurrent of this succeeding phase and the phase of Figures 1, 2 and 3commutate from the time t to the time 1 That is to say that during theinterval t to t the current of the succeeding phase will increase fromsubstantially zero to its maximum value whereas the current J of theFigures 1, 2 and 3 will decrease from their maximum value to a minimumvalue which is given by the magnetizing current of the commutatingreactor creating the low step current.

In the case of Figure l, the time t which is approximately midwaybetween the beginning and end of the low current step indicates thedesired point of contact interruption. This point is to be desired sinceit affords a certain amount of flexibility to the operating means whichoperates the contact into and out of engagement. That is to say, smallinaccuracies in this operating means will not be sufficient to move thepoint 1 out of the step interval.

In the case of Figure 2, it is seen that the point 1 which is the pointof contact interruption is beyond the end of the step created by thecommutating reactor.

This condition could be caused by any number of things such as echanicalbreaka'ge, rapid changes in electrical conditions and so on. Figure 3indicates just the opposite possibility wherein the point of contactinterruption t occurs prior to the initiatien of the low current step.

In the event of the existence of a condition as seen in Figure 2 or 3,viz. contact interruption outside of the low current protective step, itis understood that arcing will occur which arcing could be followed bycontact destruction as Well as subsequent contact destruction of otherphases of the unit. In order to prevent this, it has been the practiceto provide short circuiting devices which will short circuit theconverter contacts and the unit is subsequently disconnected from .themain power source by other circuit interrupting equipment.

In the past, however, operation of the short circuiting devices was notinitiated until after the end of the low current protective step and theoccurrence of a relatively large amount of reve'rsec'urrent through thefaultycontact. As will be shown hereinafter, my invention contemplates acircuit for initiating operation 'of' the short circuiting equipment ata time prior tothe occurrence of this relatively large magnitude ofreverse current in the event that the contact is opened prior to the lowcurrent step as is shown in Figure 3. i

Figure 4 shows the schematic View of a three-phase rectifier which isprovided with a short circuiting protective means, this short circuitingprotective means being energized by my novel circuit. More specifically,Figure 4 shows a converter which is energized by windings R, S and Twhich'could be the secondary windings of a threephase transformerenergized from an A.-C. line. In series with each of the'phases R, S andT is the main winding 1 of a commutating reactor 2, a pair of stationarycontacts 3, and the D.-C. circuit including a stabilizing choke 5 and aD.-C. load 6. The stationary contacts 3 are synchronously engaged by themovable bridging contact 7 which moves into and out of engagement withthe contacts 3 in accordance with the frequency of the A.-C. source by amotor schematically indicated as motor M. i

A short circuiter shown generally at 8 is then provided and comprises amovable winding 9 and a plurality of stationary contacts It). It is seenthat each of the contacts it} is connected to each phase in such amanner as to bypass the contacts of each phase and the D.C. load whenthe armature 9 is moved into engagement with the contacts 10.

A 'coil 11 is then shown as being provided for the short circuiter 8, itbeing understood that coil 11 could be but one coil of a complicatedmagnetic system wherein energization of the coil 11 is efiective to movearmature 9 into contact engagemen'twith the plurality of contacts 10,thus eflfecting short circuiting of these contacts. Hence by causingenergization of the coil 11 at a time in which the'point of contactinterruption does not fall within the low current protective step givenby windings 1 of commutating reactors 2, it is seen that the desiredprotection is achieved. Y Y

My novel energization circuit is comprised of permament magnets 12 whichare fastened to the movable magnets "7, windings 13 which areconstructed to have the permanent magnets 12 movable therethrough uponmovement of movable contacts 7, diodes 14-, the gas tube 16 having agrid 15, the cathode resistor 17, and condenser 18. A second gas tube 20is then provided having a grid 19, the potential of which is determinedby the potential of windings 21 of commutating reactor 2 and thedirection in which the diodes 22 are connected for current conduction. a

It is to be noted thatthis tube 20 could be. replaced by any switchingmeans having an output circuit which would include the energizing coilof a short circuiter and an input circuit for firing or triggering theswitching means which would include the measuring output ofthecommutating reactor step and the point of contact interruption.

The potential of windings 21 appears on the grid resistor 23 which isconnected to grid 19 and in series with cathode resistor 17 of gas tube16. A first source of p itive plate potential schematically shown byterminal for gas tube 16 is shown as coming through the resistor 31, theplate of the gas tube 16, the cathode resistor 17 and back to a negativepotential terminal 3112. ii i the positive plate potential for gas tube2% is by the capacitor 24 which is charged in series schematically shownpositive source terminal 32:! and resistor 32, this plate circuitincluding the plate of tube 2% and the winding 11 of the short circuiter8. ordingly, it is now seen that when the gas tube 28 fires toappropriate grid potential on the grid 13 men the winding 3.1 will beenergized and short circuiter operation will proceed.

The operation of the circuit of Figure 4 proceeds as follows: Duringmovement of the movable contact '7, the permanent magnet is moved withinthe magnet 13 to thereby produce the output potential shown in Figure 5Bfor each of the three phases. It is seen that this output potential isunidirectional in view of the blocking action of the rectifiers 14 It isfurther noted that this potential is impressed in series with acapacitor 18 which converts the potential of Figure SE to the pulse likepotential of Figure 5C. The potential of Figure 5C is then impressedacross the plate circuit of thyratron i6 and an output of similar shapeappears across the resistor 2.7. it is this potential across theresistor 17 as will be seen hereinafter which indicates the point atwhich contact interruption occurs for each of the phases and is comparedto the step interval of the ccmmutating reactor.

A measure of the commutating reactor step interval is obtained from thewindings 21 which have a voltage appearing thereacross duringunsaturation of the commutating reactors 2. The potential appearingacross the grid resistor 23 of tube 20 is seen in SA, this potentialbeing a unidirectional one in view of the blocking diodes 22.

It is now to be noted that the potential due to the windings 21 of thecommutating reactor is impressed on the grid 19 as negative potentials.The total potential on grid 19 may be seen to comprise the potential ofFigure 5A across resistor 23 as well as the potential across resistor 17which is in series with resistor 23 and is the pulse like potential ofFigure. 50. Furthermore, the potential of Figure 5C whichfis impressedacross the resistor i7 is in a direction opposite to the potentialacross the resistor 23.

Figures 6A and 6B show the operation of my. novel circuit whenthepotentials across resistors 17 and 23 are combined when the contact '7is opened in the middle of the commutating reactor step. Figure 6A morespecifically shows the contact current I and the point of contactinterruption t occurring approximately in the middle of the low currentstep. Figure 6B which is plotted on the same time axis as Figure 6A thenshows the superposition of the potential due to the step of thecommutating reactor of Figure SA as well as the potential appearingacross the grid resistor 17 of Figure 4 due to the opening of thecontact 7. e

The line marked ignition voltage in Figure 6B to which the voltages ofFigures 5A and 5C are referred to is the potential required on grid 19of gas tube 20 to fire the tube. In the case of the normal operation ofFigure 6A, it is seen that the superposition of the commutating reactorvoltage and the contact voltage are insufficient to exceed this ignitionvoltage in a positive direction since the commutating reaction voltagewhich is negative exceeds the magnitude of the voltage of resistor 17which is positive.

It is to be further noted that even if the contact open- ,ing intervalhad occurred at the. very beginning of the step where the commutatingreactor step voltage is at its lowest value, the pulse voltage of FigureC when superimposed as in Figure 68 would still not have been sufiicientto exceed the ignition voltage of gas tube 20.

When, however, as in the case of Figures 7A and 7B, the point of contactinterruption occurs prior to the commutating reactor step, then thesuperposition of the voltages appearing across resistor 23 and resistor17 will indicate that at the point or" contact interruption, the onlyvoltage present will be the voltage due to the opening of the contact 7which voltage will exceed the ignition voltage of the gas tube 2a tothereby efiect firing thereof. That is to say, when voltage appearsacross resistor 17 in the absence of an opposing voltage in resistor 23,the gas tube 26 will be ignited. Upon ignition of the gas tube 2t it isnow apparent that winding 11 ofthe short circuiter 3 will be energized,thus initiating the operation of the short circuiter for subsequentprotection of the contacts 3.

A variation of Figure 4 may be seen in Figure 8 wherein the permanentmagnet arrangement utilized for measuring the point of contactinterruption is now replaced by means of D.-C. circuits for each contactwhich circuits include the stationary contact 25, D.-C. source 26,transformer primary windings 27, secondary windings 28 and the diode 29.In place of the cathode resistor 17 of Figure 4, I now utilize aresistor which serves the same function. In the case of Figure 8, it isseen that upon contact interruption that the voltage appearing betweenthe stationary contact 25 and the movable contact 7 will appear acrossthe primary winding 27. This voltage will then be induced into thesecondary windings 28 which voltage is rectified by rectifier 29 andimpressed across the resistor 3tl. Hence the beginning of this voltagefor each phase serves to give a measure of the point at which contactinterruption takes place and operation of the complete circuit willproceed in the same manner as described above in connection with Figure4.

It is to be noted at this point that in the case of each of Figures 4and 8, that short circuiter operation will be initiated whenever thepoint of contact opening is outside of the commutating reactorprotective step, that is, if the contact is separated after the end ofthe low current protective step, then as in the case or" the prior artdevices, short circuiter operation must subsequently follow. If,however, this point of contact opening takes place before the initiationof the low current protective step, then at this point, short circuiteroperation will be initiated without having to wait for the appearance ofreverse current throughout the arcing contact.

Figure 9 shows a further embodiment of my novel invention asspecifically applied to a contact converter having one set of contactsfor making operation only and a second set of contacts for only breakingoperation. That is to say, contacts 3e operate after operation ofcontacts 3a to close the phase in which they are associated. Hence, theysee making duty only. .Sirnilarly, contacts 3a are opened prior toopening of contacts 3e and hence are subjected to breaking duty only.

In the case of Figure 9, I provide a first short circuiter system whichas in the case of the prior art is operative to cause short circuiteroperation only after the end of the low current interval. I then, hwever, provide a second circuit which is efiective to cause shortcircuiter operation when the breaking contacts 3a are opened prior tothe initiation of the low current step.

For the device which operates in the prior art manner, there is provideda current transformer 36 for each phase of the system and a rectifier 37which rectifies the three phase output of the current transformer 35.This rectified output is impressed upon the winding 38 of transductor 39while a second input to the transductor 39 is an input which isproportional to the D.-C. load current through the load 6 as is shown bythe single wire 3942 through the center of the transdsctor.

During normal operation (in the absence of reverse current in anyphase), the ampere turns due to winding 39 are suflicient to exceed theampere turns of winding 38 to thereby maintain transductor 39 saturatedin one direction. When, however, reverse current appears in any of thephases, the ampere turns of the winding 33 increases rapidly to overcomethe ampere turns of winding 39a and thereby drive transductor 39 tounsaturation. Upon reaching this unsaturated condition, a voltage willbe generated in winding 40 which voltage is effective to energizewinding 41 of short circuiter 8 to thereby cause operation of the shortcircuiter.

I then provide a second circuit which is effective to cause operation ofthe short circuiter in the event that contact separation occurs prior tothe initiation of the low current step. This circuit is seen connectedacross the breaking contact 3a, each phase being connected to arectifier 43 which is connected to energize a winding 44 of the shortcircuiter 8. The current flowing through the winding 44 during normalcontact opening conditions is as seen in the dotted portion of Figure 6Aa relatively low current which is so adjusted as to be incapable ofoperation short circuiter 8. If, however, contact opening proceedsbefore initiation of the low current step, then as is seen in the dottedportion of Figure 7A, a current of relatively high magnitude will flowthrough rectifier 43 to winding 44 of the short .circuiter 8 to causeoperation thereof. Clearly this same operation could be described inconjunction with a mechanical converter or an electromagneticallyoperated converter having a single contact for both opening and closingoperation.

Although I have described preferred embodiments of my invention, it willnow be obvious that many variations and modification may be made bythose skilled in the art. I prefer therefore to be limited, not by thespecific disclosure herein, but only by the appended claims.

We claim:

1. An energizing circuit for a short circuiter adapted to short circuita pair of cooperating contacts; said pair of cooperating contacts havinga commutating reactor connected in series therewith; said energizingcircuit comprising a first and second measuring means; said firstmeasuring means being constructed to measure the step interval of saidcommutating reactor; said second measuring means being constructed tomeasure the point of contact interruption of said pair of cooperablecontacts and circuit connections for operating said short circuiter whensaid measured point of contact interruption is outside of said measuredstep interval of said commutating reactor.

2. An energizing circuit for a short circuiter adapted to short circuita pair of cooperating contacts; said pair of cooperating contacts havinga commutating reactor connected in series therewith; said energizingcircuit comprising a first and second measuring means; and meanstocombine the outputs of said first and second measuring means; saidfirst measuring means being constructed to measure the step interval ofsaid commutating reactor; said second measuring means being constructedto measure the point of contact interruption of said pair of cooperablecontacts; said means to combine the outputs of said first and secondmeasuring means being operative to operate said short circuiter whensaid measured point of contact interruption is outside of said measuredstep interval of said commutating reactor.

3. A short circuiter for short circuiting a first pair of electricalcontacts; said short circuiter comprising a second pair of contacts andan energizing winding; said second pair of contacts being constructed tobe moved to an engaged position responsive to energization of saidenergizing winding; a commutating reactor, said commutating reactorbeing connected in series with said first pair of contacts; anenergizing circuit; said energizing circuit comprising a first andsecond measuring means; said first measuring means being constructed tomeasure the step interval of said commutating reactor; said secondmeasuring means being constructed to measure the point of contactinterruption of said first pair of cooperable contacts and circuitconnections forenergizing saidshortci'r cuiter energizing winding whensaid' measured point" of contact interruption is outside of saidmeasured'step interval of said conirnutating reactor;

4. A short cir'ciiiter for short circuiting a first pair of electricalcontacts; said short circuiter comprising a sec ond pair of contactsandan energizing'winding'; said'second'pair of contactsbeing'constructed to be moved to an engaged position'respon'sive toenergization of said energizing winding; a commutating reactor; saidcon1mutat ing reactor being connected'in's'eries with said first pair ofcontacts; an energizing circuit; a' switching means; said switchingmeanshaving" a'n output'circuit and input circuit; said output circuitbeing connected't'o sai i short circuiter energizingwinding;said inputcircuitincluriing a first means for measuring the step interval of saidcommutating reactor and a second means'for measuring the point ofcontact interruption of said second pair of contacts; said input circuitbeing operative to energize said switching means to'initiateenergizationof said energizing winding through said output circuit when saidmeasured point of contact interruption is outside of said measured stepinterval of said cornmutatingreactor;

5. A short circuiter for short circuiting a first pair of electricalcontacts; said short circuiter comprising second pair of contacts and anenergizing winding; said second pair of contacts being constructed to bemoved to an engaged position responsive to energization of saidenergizing winding; 21 eominutating reactor, said commutator reactorbeing connected in series with said first pair or" contacts; anenergizing circuit; a switching means; said switching means having anoutput circuit and an input circuit; said output circuit being connectedto said short circuiter energizing winding; said input circuit includinga first means for measuring the step interval of said commutatingreactor and a second means for measuring the point of contactinterruption of said second pair of contacts; said input circuit beingoperative to energize said switching means to initiate energization ofsaid energizing winding through said output circuit when said measuredpoint of contact interruption is outside of said meas ured step intervalof said commutating reactor; said switching means comprising a gridcontrolled gas tube; said input circuit being connected to the gridcathode circuit of said gas tube.

6. A short circuiter for short circuiting' a first pair of electricalcontacts; said short circuiter comprising a second pair of contacts andan energizing winding; said second pair of contacts being constructed tobe moved to an engaged position responsive to energization of saidenergizing winding; a commutating reactor, said commutating'reactorbeing connected in series with said first pair of contacts; anenergizing circuit; a grid controlled gas tube; said grid controlled gastube having an outputsufiicient to fire said gas tube, the net magnitudeof bothof said potentials being of too low a magnitude to fire saidtube.

7. In a contact, converter for exchanging energy be tween an A.-C.system and a DC. system; a cornmutat ing reactor and a pair ofcooperating contacts; said pair of cooperating contacts being operatedto connect said A.-C. system, D.-C. system and commutating reactor in,series in synchronism with the frequency of said A.-C.

system; a short circuiter adapted to short circuit said pair ofcooperating contacts and an energizing circuit therefor; said energizingcircuit comprising a first and second measuring means; said firstmeasuring means be= ing constructed to measure the step interval of saidcominutating reactor; said second measuring means being constructed tomeasure the point of contact'interruption' of said pair of cooperablecontacts and circuit connections for operating said short circuiter'when said measured point of contact interruption is outside of saidmeasured step interval of said commutating reactor.

8, in a contact converter for exchanging energy between an A.-C. systemand a D.-C. system; a commutating reactor and a pair of cooperatingcontacts; said pair of cooperating contacts being operated to connectsaid A.-C. system, D.-C. system and commutating reactor in series insynchronism with the frequency of said A.- C.

system; a short circuiter adapted to short circuit said pair ofcooperating contacts and an energizing Winding therefor; circuitconnections for passing contact current through said energizing windingimmediately after contact disconnection; said energizing winding beingconstructed to operate said short circuiter when the currenttherethrough is of a magnitude due to contact disconnection prior to theinitiation of step current by said commutating reactor; the magnitude ofstep current being insufiicient to energize said energizing winding foroperation of said short circuiten Busemann July 20, 1954 Owen Oct. 16,1956

